1973 Evinrude 50 hp - Shifting into gear it kills when in water, not on muffs

[marleywars]

I've read enough posts and responses to know that this has been somewhat covered by I can't find anything definitive enough to solve my problem because I've gone through the sensible test. Problem: Runs just fine on muffs. Can shift and "accelerate" in the drive-way. When under pressure/submerged in water when I shift into gear, it dogs and dies. When I bought the boat, I brought it into a mechanic because the linkage caused it to race uncontrollably. He cured it enough that I could idle thing down nicely (on muffs). I also paid him to do a carb rebuild. Compression on the 2 stroke/2 cylinder is at 135/122, seemingly good enough. New plugs, new power pack, both coils are good. Basically, I think that the pressure from the water (when submerged) causes enough backpressure to stall the engine. The bulb is full and the engine seems to get suitable gas. Ignition and firing seems adequate too. As far as I have read and understand, it could be the fuel pump (I checked and looks clean), lack of fuel (already addressed), ignition/firing (I've replaced coils and power pack that were faulty). Any suggestions would be greatly appreciated.

 

[Barnacle_Bill]

Has the idle speed been set correctly? It should be done with the boat in the water, motor running and in gear.

 

[kbait]

Try adjusting the idle mixture needle jets (front of carbs). Back pressure caused by having the exhaust in the water requires a richer mixture (counterclockwise).

Good luck!

 

[marleywars]

I have adjusted the mixture needles but only with muffs on. Thanks for the apparently simple and obvious next step to take. Don't know why I didn't think of that!

 

[marleywars]

Adjustment of the needles didn't fix the problem. Brought it out to my mechanic and he said there might be a problem in the seal in the crank shaft (or something like that) where the air/gas mixture is not balanced out properly. He said he would have to probably tear it apart to figure it out. He also said he wasn't even sure if that would be it. He is kind of at a loss so I just took the boat home and am trying to come up with another plan. Another Seafoam run-through is the best I can come up with. All the carb and needle adjustments have apparently to him have been tried. At a loss..........

 

[marleywars]

Adjustment of the needles didn't fix the problem. Brought it out to my mechanic and he said there might be a problem in the seal in the crank shaft (or something like that) where the air/gas mixture is not balanced out properly. He said he would have to probably tear it apart to figure it out. He also said he wasn't even sure if that would be it. He is kind of at a loss so I just took the boat home and am trying to come up with another plan. Another Seafoam run-through is the best I can come up with. All the carb and needle adjustments have apparently to him have been tried. At a loss..........

 

[marleywars]

Could there be some sort of exhaust obstruction between the power head and the mid-section??????

 

[GA_Boater]

Did you try to adjust the needles with the boat in the water and idling in gear?

 

[marleywars]

I can't get it in gear in the water. Again, no problem with the muffs but in the water, I start it in neutral, idle it down, and as soon as I start to engage the prop (forward or reverse), it stalls. Any suggestions would help, otherwise, after two summers of working on this thing, I may have to part ways.

 

[racerone]

On a hose there is no load on the motor !---It will sound fine running on one cylinder and it will rev up in gear.----In gear on the trailer is really still nuetral as the prop does not need to do anything.-------Check and make sure it is running on both cylinders and do a compression test.

 

[marleywars]

I did a compression test when I first bought it and even not too long ago. Both cylinders are good at 135 & 125. I replaced the power pack and swapped out the lower coil. Both fire. Could the timing be off just enough to cause this problem? Could there be any obstruction outside the cylinder via the exhaust channel that could be dogging this thing down? Part that sucks is that a marine mechanic, albeit a totally inept one after my experience with him, didn't offer any definitive advice or fix. Again, he just said it may be a seal.

 

[marleywars]

I removed the motor from the boat and brought it inside. I removed the exhaust cover and noticed significant carbon build-up on the plate but not enough, one would think, to prevent the exhaust to leave the engine. That being said, my plan is to remove all the carbon that I can and put new gaskets on the plate. On a side note, the 15 screws that I had to remove the plate, a number of them on the right side/nearer the rear of the engine, showed signs of being exposed to water (leaky gasket?) and were a bit corroded and more difficult to remove. Could a not fully-sealed gasket contribute to the motor killing when put into gear? I really appreciate any feedback!

 

[greasemonkeyjm]

I bought a 1987 Evinrude 48SPL a couple weeks ago, had 122/125 pounds of compression, it would idle on the hose, but had a little stutter to it, but in the water it would either die, or it would idle up and run away with itself, tried everything that was suggested, then tore the engine down, it ended up having 2 scored pistons and cylinder walls.

 

[marleywars]

I did notice that the cylinder walls had some scoring to it. I guess I don't know if any scoring is acceptable or I have to concedes a total rebuild. What is your plan with your engine? Again, if the compression is good, does the minor scoring mean that much?

 

[greasemonkeyjm]

I am actually getting my cylinders bored out and am going to replace the pistons and rebuild it, mine has the worst scoring around the exhaust ports

 

[marleywars]

I guess I should bring my engine to my mechanic and get his opinion on the degree of scoring that I have. I would have simply just replaced the gaskets and reassembled. I might as well get it properly diagnosed so I don't waste any more time. Your input was helpful, thanks.

 

[marleywars]

Got back from my mechanic and he looked at the top cylinder/piston and said it should be bored and replaced. Guess I'm all in. Winter is soon coming here in northern MN so I have plenty of time to work on this "science project" of mine. Thanks for your help and good luck with yours.